Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), and flash memory.
Flash memory devices have developed into a popular source of non-volatile memory for a wide range of electronic applications. Flash memory devices typically use a one-transistor memory cell that allows for high memory densities, high reliability, and low power consumption. Common uses for flash memory include personal computers, personal digital assistants (PDAs), digital cameras, and cellular telephones. Program code and system data such as a basic input/output system (BIOS) are typically stored in flash memory devices for use in personal computer systems.
As the performance and complexity of electronic systems increase, the speed of the system memory needs to increase as well. However, one of the disadvantages of flash memory is the slow programming and erase speeds. Typical prior art programming uses either Fowler-Nordheim tunneling or hot electron injection to move a charge from a channel in the substrate onto the floating gate. The mechanism by which they tunnel through the oxide/insulator layer damages the layer. This limits the number of times that a flash memory device can be programmed reliably before the dielectric wears out and loses its insulating properties.
The flash road map requires a memory cell structure change due to the scaling limitations of the floating gate technology. The floating gate stack has a problem with capacitive coupling to neighboring cells causing disturb problems. By lowering the stack height, the capacitance can be reduced. One approach is to eliminate the floating gate and use a SONOS approach to storing charge in the dielectric layer itself. A second approach that enhances the SONOS structure is to add nano-crystals under the word line poly.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a memory device that operates faster and has a longer life.